Commit-ID: 39a4d9ca77a31503c6317e49742341d0859d5cb2 Gitweb: http://git.kernel.org/tip/39a4d9ca77a31503c6317e49742341d0859d5cb2 Author: Jason Low <jason.low2@xxxxxx> AuthorDate: Wed, 23 Apr 2014 18:30:35 -0700 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitDate: Wed, 7 May 2014 13:33:53 +0200 sched/fair: Stop searching for tasks in newidle balance if there are runnable tasks It was found that when running some workloads (such as AIM7) on large systems with many cores, CPUs do not remain idle for long. Thus, tasks can wake/get enqueued while doing idle balancing. In this patch, while traversing the domains in idle balance, in addition to checking for pulled_task, we add an extra check for this_rq->nr_running for determining if we should stop searching for tasks to pull. If there are runnable tasks on this rq, then we will stop traversing the domains. This reduces the chance that idle balance delays a task from running. This patch resulted in approximately a 6% performance improvement when running a Java Server workload on an 8 socket machine. Signed-off-by: Jason Low <jason.low2@xxxxxx> Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: daniel.lezcano@xxxxxxxxxx Cc: alex.shi@xxxxxxxxxx Cc: preeti@xxxxxxxxxxxxxxxxxx Cc: efault@xxxxxx Cc: vincent.guittot@xxxxxxxxxx Cc: morten.rasmussen@xxxxxxx Cc: aswin@xxxxxx Cc: chegu_vinod@xxxxxx Link: http://lkml.kernel.org/r/1398303035-18255-4-git-send-email-jason.low2@xxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> --- kernel/sched/fair.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 051903f..28ccf50 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6713,7 +6713,6 @@ static int idle_balance(struct rq *this_rq) if (sd->flags & SD_BALANCE_NEWIDLE) { t0 = sched_clock_cpu(this_cpu); - /* If we've pulled tasks over stop searching: */ pulled_task = load_balance(this_cpu, this_rq, sd, CPU_NEWLY_IDLE, &continue_balancing); @@ -6728,7 +6727,12 @@ static int idle_balance(struct rq *this_rq) interval = msecs_to_jiffies(sd->balance_interval); if (time_after(next_balance, sd->last_balance + interval)) next_balance = sd->last_balance + interval; - if (pulled_task) + + /* + * Stop searching for tasks to pull if there are + * now runnable tasks on this rq. + */ + if (pulled_task || this_rq->nr_running > 0) break; } rcu_read_unlock(); -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html